A free form of lurasidone and an acid addition salt thereof are known to have psychotropic activities and are effective as therapeutic agents, particularly for schizophrenia or senile dementia, etc. Senile dementia is broadly classified into Alzheimer's dementia and cerebrovascular dementia, and it can be said that the two make up about 80% of senile dementia. In accordance with rapid aging of the population, the number of patients with dementia tends to increase and among the population of 65 or more years old about 7% is estimated to be suffered from dementia in Japan, and hence, developments of effective therapeutic agents for dementia are desired. Lurasidone is known to be administered orally or parenterally, and methods for administering in the form of a solid preparation, such as tablet or capsule, or as a liquid preparation for an oral preparation and as an injection or suppository for a parenteral preparation are disclosed in Patent Document 1. Administration of an oral preparation, particularly a solid preparation, is usually believed to be the most common and preferable in treatment for many diseases. However, patients with schizophrenia or senile dementia individually have wide-ranging symptoms, and hence, it is sometimes not sufficient to treat such patients only with oral solid preparations, for example in case of administration to patients with schizophrenia in acute stage, patients of drug refusal or aged patients.
If a free form of hardly-soluble lurasidone or an acid addition salt thereof can be prepared in the form of a solution-type preparation, it may be usable in wider-ranging preparations including parenteral preparations (e.g. injections), or oral liquid preparations, and it may provide various, convenient and effective methods for treatment of much more patients. However, since lurasidone or a free form thereof has a solubility of less than several μg/mL in water, it has hitherto been very difficult to prepare an aqueous solution-type preparation containing a high concentration of lurasidone or a free form thereof. Additionally, no method for solubilizing lurasidone and a free form thereof has been known so far. In case of using a solution-type preparation for parenteral administration such as an injection, there are potential problems such as local irritation, hemolysis, neurotoxicity, etc. depending on the kinds of organic solvents, and hence, the dose of the organic solvent or contents in a solution are limited, and accordingly, it is required to reduce the amount of the organic solvent.    Patent Document 1: JP2800953